This invention relates to a simple torquechange detecting system used for a feedback control device for controlling the ignition timing or air-fuel ratio in order to achieve the optimum engine operating conditions by detecting the change in the torque generated in the internal combustion engine.
The ignition timing or air-fuel ratio of the internal combustion engine must be determined in accordance with the engine conditions in order to attain the optimum engine operating conditions.
In conventional systems, the engine speed is detected by the centrifugal advancing mechanism and the negative intake pressure by the vacuum advancing mechanism, so that such factors representative of the engine conditions are generally used to determine the ignition timing. From the viewpoint of engine efficiency and fuel cost, it is considered best to effect ignition at the minimum advance for best torque (MBT), and the ignition timing must be changed to conform with MBT in accordance with the engine conditions.
In the above-mentioned conventional systems, however, the ignition timing is programmed at an average on the basis of the results of the tests on the internal combustion engines, and therefore the ignition timing is considerably displaced from the actual MBT. The programmed ignition point differs from the actual ignition point due to the atmospheric condition or variations in individual engine characteristics. It is difficult to correct such differences in actual practice, with the result that ignition often fails at the required advance angle. For correction of the difference in ignition point, the corrective factors include the number of revolutions par unit time, negative intake pressure, temperature and other various environmental conditions. Further, MBT is undergoing a constant change. Considering all these corrective factors results in a high system cost on the one hand and complicates the system on the other hand, thereby leading to the disadvantage of lack of a practical value. Furthermore, there is yet no effective means for correcting the change in engine characteristics with time.
Also, it is generally known that if the amount of fuel is fixed, the torque increases for an improved saving of fuel cost, the leaner the air-fuel ratio is made by addition of air.
Thus it is desirable to maintain the air-fuel ratio on the lean side as far as possible in order to improve the saving of fuel costs. If the air-fuel ratio exceeds the combustion limit on the lean side, however, a misfire occurs thus reducing the torque.
The combustion limit changes for different engines, or with valve timing or time, and therefore the actual air-fuel ratio is unavoidably programmed on the rich side considerably far from the combustion limit determined experimentally.
In order to obviate such problems, a feedback control may be employed to attain the ignition timing as near as MBT and the air-fuel ratio as near as the combustion limit on the lean side by detecting the change in torque generated by the engine. In spite of this, there has not yet been developed any effective means for feedback control which is compact and low in cost, for detecting the change in the torque making up a factor of feedback.
A conventional detecting device of this type is mounted on the output shaft of the engine and operates in such a manner that the engine torque is detected as a torsion of the torque transmitting shaft which is generated in transmitting the torque to a load such as the wheel shaft. Other conventional devices for detecting the torsion electrically include a strain gauge system in which the electrical resistance changes with strain, the magneto-striction type in which the magnetic characteristics of the magneto-striction tube change, and the phase difference type in which the out-of-phase condition between two points of the shaft is detected. The main object of these device is to detect the torque as an engine performance test. They are configured for measurement of the engine output, are great in weight, complicated in construction, and high in cost. For this reason, it is practically difficult to mount them on a vehicle for feedback control. Even if they can be mounted technically on the vehicle, their applications are limited due to their high cost. Their problems will be described below specifically.
(1) In all the systems mentioned above, a detector is arranged midway on the engine crank shaft and the load drive transmission shaft (propeller shaft). They are thus different from an ordinary torque transmission mechanism and therefore must be reconstructed.
(2) The output shaft of the engine must transmit high r.p.m. and high torque. Therefore, the detector arranged midway must have a strength sufficiently high to stand the revolution load. Thus it becomes large in weight, high in cost on the one hand and a signal must be taken out of the rotational member on the other hand. Also, it must be provided with signal transmission systems such as signal AC coupling, resulting in structural complication and high cost.
(3) The principle of the detector is based on the detection of the torsion of the shaft. If the detector shaft is short, strain is so small that the detection accuracy is deteriorated, and therefore the length of the detector shaft must be lengthened (generally, 30 to 40 cm) to assure an improved accuracy.
The torque detecting device of this type, therefore, is only practicable for the purpose of a test in which the increase in engine length or weight or engine reconstruction is permitted. On the other hand, it is practically difficult to carry it on a vehicle as a detector means for feedback control for its high cost, weight and size.